1. Field of the Invention
The field of this disclosure is horology. It relates more particularly to a timepiece movement comprising a mechanism arranged to drive an indicator member in a stealthy rotational movement activated periodically, with a predefined period.
In this text, the use of the term “stealthy” in relation to the notion of period should be understood to relate to an event whose duration is much shorter than this period. A non-restrictive example would be that the rotational movement is activated once every minute and each activation lasts for three seconds.
More precisely, the horological movement comprises a going train, the mechanism also comprising                a first wheel-and-pinion unit comprising a first wheel at least indirectly in engagement with the going train,        a second wheel-and-pinion unit mounted coaxially with the first wheel-and-pinion unit, having at least one stop region and a second wheel, these being integral in rotation, while a second cinematic connection connects the second wheel to the indicator member,        an elastic member connecting the first wheel-and-pinion unit to the second wheel-and-pinion unit in such a way that its degree of tension is a function of the respective angular positions of the first and second wheel-and-pinion units, and        locking means designed to engage with the stop region of the second wheel-and-pinion unit to prevent the latter from rotating between two successive movements of the indicator member.        
In a preferred exemplary embodiment of the invention, the indicator member may carry a sign, which may or may not represent time information of some kind, this sign being made visible to a user through an opening in the dial of the corresponding timepiece, but only during at least part of the stealthy rotational movement.
2. Description of Related Art
Numerous jumping mechanisms are known in the prior art, particularly in movements for driving one or other of the time-indicating members in a jumping or intermittent manner. For instance, numerous movements of the so-called “dead seconds” type are known in which the seconds indicator member is driven in jumps occurring at a lower frequency than that of the time base of the movement, typically an escapement. U.S. Pat. No. 2,591,876 discloses one embodiment of a movement of this type.
These mechanisms usually employ two wheels, one driven continuously by the going train, and the other intermittently only, by the relaxing of an elastic member which is tensioned between two successive jumps, by the continuous rotation of the first wheel. Locking means similar to an escapement anchor are conventionally used to hold back the second wheel between two movements, by interaction with its teeth.
However, these mechanisms sometimes take up a great deal of space, are often sensitive to shocks, and can transmit only very sudden movements to the intermittently driven indicator member.